What is the difference between reflective and reflexive?
Reflection might lead to insight about something not noticed in time, pinpointing perhaps when the detail was missed. Reflexivity is finding strategies to question our own attitudes, thought processes, values, assumptions, prejudices and habitual actions, to strive to understand our complex roles in relation to others.
What is reflectivity formula?
Reflectivity ρ is the ratio of the radiation flux Φr reflected by a sample surface to the incident radiation flux Φi: Sometimes the term “reflectivity” is understood as the ratio of the mentioned fluxes when the sample reflects volumetrically including its interior if it is semitransparent to thermal radiation.
What is absorptivity and reflectivity?
Absorptivity (α) is a measure of how much of the radiation is absorbed by the body. Reflectivity (ρ) is a measure of how much is reflected, and transmissivity (τ) is a measure of how much passes through the object. Note that the angle at which the incident radiation hits the surface has an effect on these parameters.
Which one is true regarding gases reflectivity is unity?
Explanation: For the opaque body, sum of absorptivity and reflectivity is unity.
What is J in radiation?
Radiosity J: total radiation energy streaming from a surface, per unit area per unit.
Which one is having the highest value of fouling factor?
Which one is having the highest value of fouling factor? Explanation: Fouling factor for liquid gasoline is 0.0008 while that of clean river, sea water and distilled water are 0.0002, 0.0001 and 0.0001 respectively. Fouling factor = 1/hS. 2.
What is a fouling factor?
The fouling factor represents the theoretical resistance to heat flow due to a build-up of a layer of dirt or other fouling substance on the tube surfaces of the heat exchanger, but they are often overstated by the end user in an attempt to minimize the frequency of cleaning.
How do you calculate fouling rate?
Typical Fouling Factors
- Alcohol vapors : Rd = 0.00009 (m2K/W)
- Boiler feed water, treated above 325 K : Rd = 0.0002 (m2K/W)
- Fuel oil : Rd = 0.0009 (m2K/W)
- Industrial air : Rd = 0.0004 (m2K/W)
- Quenching oil : Rd = 0.0007 (m2K/W)
- Refrigerating liquid : Rd = 0.0002 (m2K/W)
- Seawater below 325 K : Rd = 0.00009 (m2K/W)
What is the value of fouling factor for sea water?
| Water | Fouling Resistance | |
|---|---|---|
| River Water (minimum) | 0.002 | 0.001 |
| River Water (average) | 0.003 | 0.002 |
| River Water (muddy or silty) | 0.003 | 0.002 |
| Sea Water | 0.0005 | 0.0005 |
What is a high fouling factor?
The fouling factor represents the theoretical resistance to heat flow due to a build-up of a layer of dirt or other fouling substance on the tube surfaces of the heat exchanger, but they are often overstated by the end user in an attempt to minimise the frequency of cleaning. …
Does fouling increase overall heat transfer coefficient?
Fouling or dirt factor is used for calculation of the overall heat transfer coefficient of a heat exchanger. Consider the following equation. It is clear from the equation that, as the fouling factors (either on shell or tube side) increase, overall heat transfer coefficient will decrease.
How does fouling factor affect heat transfer?
The deposition of any undesired material on heat transfer surfaces is called fouling. Fouling increases the overall thermal resistance and lowers the overall heat transfer coefficient of heat exchangers. Fouling also impedes fluid flow, accelerates corrosion and increases pressure drop across heat exchangers.
What is overall heat transfer coefficient definition?
The overall heat transfer coefficient is a measure of the overall ability of a series of conductive and convective barriers to transfer heat. It is commonly applied to the calculation of heat transfer in heat exchangers, but can be applied equally well to other problems.
How do you prevent heat exchanger scaling?
For a heat exchanger with a temperature above 70°C on the hot side and/or very hard water (and hence a danger of scaling), the pressure drop should be increased as much as possible on the cold water side and reduced on the hot side.
How do you detect fouling in a heat exchanger?
The off-line and on-line methods are build up by dividing the heat exchanger into sections. The states (temperatures) in the sections are represented with physical equations and the Kalman filter is used to estimate the states. Fouling detection is done by monitoring parameters of the model.
How fouling affects the heat transfer rate and pressure drop?
Amount of layer deposition has direct impact on heat transfer and pressure drop, as it affect on physical dimension of shell and tubes of heat exchanger. The heat transfer surface fouls during operation, resulting in increased thermal resistance and often an increase in the pressure drop and pumping power.
What is pressure drop in heat exchanger?
When a flow is disturbed, a pressure drop (ΔP) is created, i.e. the flow pressure at the beginning of a passage is higher than at its end. Pressure drop is a phenomenon with both positive and negative consequences for the heat transfer process.
How does fouling influence the required size of a heat exchanger?
In addition, increased surface roughness due to fouling will increase frictional resistance to flow. Such effects inevitably lead to an increase in the pressure drop across the heat exchanger, which is required to maintain the flow rate through the exchanger, and may even lead to flow blocks.